The objective of this proposal is to evaluate the possible role of progesterone, estrogens, oxytocin, and prostaglandins in the initiation of parturition in women. On the basis of considerable evidence, we propose that one or most probably a combination of these hormones may act either directly on the myometrium to affect myometrial contractions, or they may act in decidua to increase the production of prostaglandins which ultimately trigger myometrial contraction. To test these hypotheses in women, two experimental approaches will be followed. We will first determine possible changes in the levels of estrogen, progesterone, and oxytocin receptors in the myometrium and decidua with advancing gestation. Both cytoplasmic and nuclear estrogen and progesterone receptors will be measured. The levels of estradiol, estrogen, and progesterone will also be determined in plasma, myometrium, and decidua of the same patients. Our second approach will be to investigate the regulation of prostaglandin production by decidua. The effects of estrogen, antiestrogen, progesterone, and oxytocin on prostaglandin synthesis and release will be examined in decidua and myometrium in organ culture. To test the possibility that estrogens and progesterone may modulate decidual sensitivity to oxytocin by regulating the levels of oxytocin receptors, the effect of oxytocin on prostaglandin synthesis and release and the levels of oxytocin receptors will be determined before and after tissue exposure to estrogen, antiestrogen, and progesterone.